fixp-arith: convert comments to kernel-doc format

fixp-arith: convert comments to kernel-doc format

Insert a hyphen ('-') in 2 places to prevent kernel-doc warnings:

Warning: include/linux/fixp-arith.h:42 This comment starts with '/**',
 but isn't a kernel-doc comment.
 * __fixp_sin32() returns the sin of an angle in degrees
Warning: include/linux/fixp-arith.h:66 This comment starts with '/**',
 but isn't a kernel-doc comment.
 * fixp_sin32() returns the sin of an angle in degrees

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20260731050625.455556-1-rdunlap@infradead.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>