Fixes a false positive from might_sleep(). The reservation object is freshly
initialized, so nobody else can hold the mutex but the function is
called from atomic context.

v2: Correctly invert the check as well.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>