Improve the error messages and clean up redundant code.
[1] remove redundant next_sym->name checks
If 'next_sym' is a choice, the first 'if' block is executed. In the
subsequent 'else if' blocks, 'next_sym" is not a choice, hence
next_sym->name is not NULL.
[2] remove redundant sym->name checks
A choice is never selected or implied by anyone because it has no name
(it is syntactically impossible). If it is, sym->name is not NULL.
[3] Show the location of choice instead of "<choice>"
"part of choice <choice>" does not convey useful information. Since a
choice has no name, it is more informative to display the file name and
line number.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
d5afb4824f