powerpc/signal32: Remove ifdefery in middle of if/else in sigreturn()

In the same spirit as commit f1cf4f93 ("powerpc/signal32: Remove
ifdefery in middle of if/else")

MSR_TM_ACTIVE() is always defined and returns always 0 when
CONFIG_PPC_TRANSACTIONAL_MEM is not selected, so the awful
ifdefery in the middle of an if/else can be removed.

Make 'msr_hi' a 'long long' to avoid build failure on PPC32
due to the 32 bits left shift.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a4b48b2f0be1ef13fc8e57452b7f8350da28d521.1616151715.git.christophe.leroy@csgroup.eu