crypto: acomp - repair kernel-doc warnings

crypto: acomp - repair kernel-doc warnings

Correct kernel-doc:
- add the @extra function parameter
- add "_extra" to the mismatched function name
- spell the "cmpl" parameter correctly

to avoid these warnings:

Warning: include/crypto/acompress.h:251 function parameter 'extra' not
 described in 'acomp_request_alloc_extra'
Warning: include/crypto/acompress.h:251 expecting prototype for
 acomp_request_alloc(). Prototype was for acomp_request_alloc_extra()
 instead
Warning: include/crypto/acompress.h:327 function parameter 'cmpl' not
 described in 'acomp_request_set_callback'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>