mips/oprofile: Fix fallthrough placement

We want neither
"
include/linux/compiler_attributes.h:201:41: warning: statement will never
be executed [-Wswitch-unreachable]
  201 | # define fallthrough __attribute__((__fallthrough__))
      |                      ^~~~~~~~~~~~~
"
nor
"
include/linux/compiler_attributes.h:201:41: warning: attribute
'fallthrough' not preceding a case label or default label
  201 | # define fallthrough __attribute__((__fallthrough__))
      |                      ^~~~~~~~~~~~~
"

It's not worth adding one more macro. Let's simply place the fallthrough
in between the expansions.

Fixes: c9b02990 ("MIPS: Use fallthrough for arch/mips")
Cc: stable@vger.kernel.org
Signed-off-by: He Zhe <zhe.he@windriver.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>