[Nit] bying -> being

TEST=None

Change-Id: Ib7ac7ecb6b2223c35ed0bf1c007e4bc8b39e464c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/184263
Commit-Queue: Clement Skau <cskau@google.com>
Reviewed-by: Clement Skau <cskau@google.com>
diff --git a/runtime/vm/constants_arm64.h b/runtime/vm/constants_arm64.h
index e44ab62..8227d64 100644
--- a/runtime/vm/constants_arm64.h
+++ b/runtime/vm/constants_arm64.h
@@ -325,7 +325,7 @@
 const RegList kAbiArgumentCpuRegs =
     R(R0) | R(R1) | R(R2) | R(R3) | R(R4) | R(R5) | R(R6) | R(R7);
 #if defined(TARGET_OS_FUCHSIA)
-// We rely on R18 not bying touched by Dart generated assembly or stubs at all.
+// We rely on R18 not being touched by Dart generated assembly or stubs at all.
 // We rely on that any calls into C++ also preserve R18.
 const RegList kAbiPreservedCpuRegs = R(R18) | R(R19) | R(R20) | R(R21) |
                                      R(R22) | R(R23) | R(R24) | R(R25) |