bpf: fix bpf expression parsing regression in GAS

bpf: fix bpf expression parsing regression in GAS

As a result of a switch instead of an if, as would issue non-specific
error messages when it encountered an operand it could not parse in bpf.
This patch fixes that regression and adds a test to prevent it from
reoccurring.

Tested for bpf-unknown-none on x86_64-redhat-linux.

gas/ChangeLog:

	* config/tc-bpf.c (parse_expression): Change switch to if so that error
	* condition is handled.
	* testsuite/gas/bpf/bpf.exp: Invoke new test.
	* testsuite/gas/bpf/indcall-badoperand.d: New test.
	* testsuite/gas/bpf/indcall-badoperand.l: New test.
	* testsuite/gas/bpf/indcall-badoperand.s: New test.