math64.h: kernel-docs: Convert some markups into normal comments

There are several functions at math64.h that are also
defined at div64.c. As both are included at kernel-api.rst,
Sphinx 3.x complains about symbol duplication:

./lib/math/div64.c:73: WARNING: Duplicate C declaration, also defined in 'core-api/kernel-api'.
Declaration is 'div_s64_rem'.
./lib/math/div64.c:104: WARNING: Duplicate C declaration, also defined in 'core-api/kernel-api'.
Declaration is 'div64_u64_rem'.
./lib/math/div64.c:144: WARNING: Duplicate C declaration, also defined in 'core-api/kernel-api'.
Declaration is 'div64_u64'.
./lib/math/div64.c:172: WARNING: Duplicate C declaration, also defined in 'core-api/kernel-api'.
Declaration is 'div64_s64'.

In order to avoid Sphinx warnings about duplication, change the kernel-doc
markups to just comments at math64.h.

Reviewed-by: Vincenzo Frascino <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

include/linux/math64.h

···
 	return dividend / divisor;
 }
 
-/**
+/*
  * div_s64_rem - signed 64bit divide with 32bit divisor with remainder
  * @dividend: signed 64bit dividend
  * @divisor: signed 32bit divisor
···
 	return dividend / divisor;
 }
 
-/**
+/*
  * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
  * @dividend: unsigned 64bit dividend
  * @divisor: unsigned 64bit divisor
···
 	return dividend / divisor;
 }
 
-/**
+/*
  * div64_u64 - unsigned 64bit divide with 64bit divisor
  * @dividend: unsigned 64bit dividend
  * @divisor: unsigned 64bit divisor
···
 	return dividend / divisor;
 }
 
-/**
+/*
  * div64_s64 - signed 64bit divide with 64bit divisor
  * @dividend: signed 64bit dividend
  * @divisor: signed 64bit divisor