powerpc/ftrace: Style cleanup in ftrace_mprofile.S

Add some line breaks to better match the file's style, add
some space after comma and fix a couple of misplaced blanks.

Suggested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/973506292d0c7b05c06530c8e11803ce38e5eda2.1644949750.git.christophe.leroy@csgroup.eu