Fix typos found by codespell

- Typos were found by codespell v1.17.0.dev0 (commit 44fea6d)
- Command used:
  codespell -q 2 \
  -L ba,bloc,blocs,doubleclick,dur,fille,frmat,numer,optin,passtime \
  -L pres,strack,te,tim,tre,uint,whn \
  --skip="*.de-DE.resx,./Bwg*,./Freedb,./MusicBrainz,./ProgressODoom" \
  --skip="./ThirdParty"

CUETools.CLParity/matlab/Errors_And_Erasures_Test.m

@@ -28,7 +28,7 @@ t = h/2
 
 %*** Generate the Galois Field and Generator polynomial ***
 
-% This step is neccessary for Matlab.  Here we create the Galois Field which is used for
+% This step is necessary for Matlab.  Here we create the Galois Field which is used for
 % computations of the Reed-Solomon code
 
 

CUETools.CLParity/matlab/RS_E_E_DEC.m

@@ -12,7 +12,7 @@ function DECODED = RS_E_E_DEC(received, erasures,n,k,t,h,g,field);
 
 %syndrome calculation
 S = [];
-%Subtitute alpha^i in received polynomial - Lin + Costello p.152 eq. 6.13
+%Substitute alpha^i in received polynomial - Lin + Costello p.152 eq. 6.13
 for ii = 1:2*t
     S(ii)= -Inf;
     for cc = 1:n
@@ -21,7 +21,7 @@ for ii = 1:2*t
 end
 %S
 
-%Test if syndrome  = 0, if syndrome equals 0, assume that no errors occured
+%Test if syndrome  = 0, if syndrome equals 0, assume that no errors occurred
 for i = 1:2*t
     test_pol(i) = -Inf;
 end
@@ -78,7 +78,7 @@ else
     else
         for i = 1:length(S_M)
             if (S_M(i) ~= -Inf)
-                flag = 1;     %Other errors occured in conjunction with erasures
+                flag = 1;     %Other errors occurred in conjunction with erasures
             end
         end
     end

CUETools.CLParity/matlab/gfsubstitute.m

@@ -1,7 +1,7 @@
 function sum = gfsubstitute(polynomial,value,terms,n,field)
 
 %use: gfsubstitute(polynomial,value,terms,n,field)
-%Subtitute i^value in polynomial
+%Substitute i^value in polynomial
 %the number of terms in polynomial
 %n = n of the decoder