mm/early_ioremap.c: improve the execution efficiency of early_ioremap_setup()

Reduce the number of invalid loops of the function early_ioremap_setup()
to improve the efficiency of function execution

Link: https://lkml.kernel.org/r/CACZJ9cU6t5sLoDwE6_XOg+UJLpZt4+qHfjYN2bA0s+3y9y6pQQ@mail.gmail.com


Signed-off-by: LiamNi <zhiguangni01@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>