common: bootm: check return value of strict_strtoul

common: bootm: check return value of strict_strtoul

Before continue, check return value of strict_strtoul.

Signed-off-by: Peng Fan <[email protected]>
Cc: Albert Aribaud <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Jan Kiszka <[email protected]>
Cc: Joe Hershberger <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: York Sun <[email protected]>
Cc: Tom Rini <[email protected]>
Reviewed-by: Simon Glass <[email protected]>