* itbl-ops.c (itbl_get_reg_val): Add pval parameter. Return
indication of success rather than a value.
(itbl_get_val): Likewise.
(itbl_get_field): Use strcspn. Change delimiters to include
parens.
* itbl-ops.h (itbl_get_reg_val): Update declaration.
(itbl_get_val): Likewise.
* config/tc-mips.c (mips_ip): Update call to itbl_get_reg_val.