celledges: Use b_width_capped for left shifts

`b_width_capped` already exists for preventing arithmetic overflow, limiting the value of `b_width` to 30.  This just changes the left shifts to also use it.
The caveat of incorrect results for extremely large values of `a_width` still applies, as does the improbability of that actually happening.
This fixes #4844 (or at least, the floating point exception; the circuit still isn't valid but I think that's fine).

kernel/celledges.cc

@@ -253,13 +253,13 @@ void shift_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
 				if (a_width == 1 && is_signed) {
 					int skip = 1 << (k + 1);
 					int base = skip -1;
-					if (i % skip != base && i - a_width + 2 < 1 << b_width)
+					if (i % skip != base && i - a_width + 2 < 1 << b_width_capped)
 						db->add_edge(cell, ID::B, k, ID::Y, i, -1);	
 				} else if (is_signed) {
-					if (i - a_width + 2 < 1 << b_width)
+					if (i - a_width + 2 < 1 << b_width_capped)
 						db->add_edge(cell, ID::B, k, ID::Y, i, -1);
 				} else {
-					if (i - a_width + 1 < 1 << b_width)
+					if (i - a_width + 1 < 1 << b_width_capped)
 						db->add_edge(cell, ID::B, k, ID::Y, i, -1);
 				}
 			// right shifts