doc: fix typo in the description of %unmacro
doc: fix typo in the description of %unmacro

The description of %unmacro used %unmacro in a place which should
obviously have been %macro.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

Distrotech/nasm,turingstudio/nasm,Distrotech/nasm,techkey/nasm,projedi/nasm,techkey/nasm,projedi/nasm,letolabs/nasm,Distrotech/nasm,letolabs/nasm,turingstudio/nasm,letolabs/nasm,turingstudio/nasm,techkey/nasm,techkey/nasm,techkey/nasm,projedi/nasm,projedi/nasm,projedi/nasm,Distrotech/nasm,turingstudio/nasm