lib: sbi: Don't check SBI error range for legacy console getchar

The legacy console getchar SBI call returns character value in
the sbiret.error field so the "SBI_SUCCESS < ret" check in
sbi_ecall_handler() results in unwanted error prints for the
legacy console getchar SBI call. Let's suppress these unwanted
error prints.

Fixes: 67b2a408

 ("lib: sbi: sbi_ecall: Check the range of
SBI error")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>