powerpc/oprofile: fix spelling mistake "contex" -> "context"

There is a spelling mistake in a pr_debug message. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200804174316.402425-1-colin.king@canonical.com